Modelling heat production in group-housed growing pigs exposed to ambient temperatures ranging between 12 and 29°C

The effects of ambient temperature (T, 12 to 29°C), body weight (BW, 30 to 90 kg) and metabolisable energy (ME, kJ/j) intake on components of energy balance were studied in seven groups of Piétrain x Large White barrows kept in a respiratory chamber. In experiment 1 (three groups), T varied in a cyclic way from 22 to 12°C and 12 to 22°C with three or four consecutive days at 22, 19, 16, 14 or 12°C. Similarly, in experiment 2 (three groups), T varied from 19 to 29°C and 29 to 19°C with three or four consecutive days at 19, 22, 25, 27 or 29°C. In both experiments, pigs were offered feed ad libitum. In experiment 3, pigs (group 7) were exposed to the thermic conditions of experiment 1 but their feed allowance was adjusted on a BW basis on the ad libitum intake recorded at 19 and 22°C in experiment 1. Five groups were studied successively between 30 and 60 kg and between 60 and 90 kg, two groups between 45 and 75 kg. The O2 and CO2 concentrations, physical activity and feed intake were simultaneously measured and used to calculate total heat production (HPtot), HP due to physical activity (HPact), and thermic effect of feed (TEF). Non linear equations for prediction of HPtot and its components according to BW, T and ME intake are proposed and evaluated according to literature values. Results indicate that all components of HP were proportional to BW0.60. The estimated lower critical temperature was 24°C. Values for the feed cost of thermoregulation in pigs are proposed.